Optical image stabilizer with improved magnetic sensitivity

ABSTRACT

A lens driving device that is based on a Voice Coil Actuator (VCA) structure and provides the auto-focusing and optical image stabilization (OIS) functions. These two functions can be realized by a common magnet scheme, or a separate magnet scheme. Also, the present invention provides an improved structure for the lens driving device to enhance the function of OIS thereof. By arranging a magnetic enhancement device below the OIS coils in the lens driving device, the magnetic driving force of the OIS coils and magnetic induction of the Hall sensors, if present, can be enhanced, and the magnetic sensitivity thereof may be also improved.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationNo. 61/836,038, filed Jun. 17, 2013, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a VCA-based lens driving device, andmore particularly, to a VCA-based lens driving device that enables theauto-focusing (AF) and the optical image stabilization (OIS).

2. Description of the Prior Art

The optical image stabilization (OIS) with a common magnet scheme hasbeen developed as a solution of anti-shaking for a conventional lensdriving device. Driving two sets of coils, e.g. the auto-focusing (AF)coil and the OIS coils, with a common magnet set to adjust the lensassembly makes the lens driving device compact, and is thus gettingwidely applicable for enhancing the image quality. Nevertheless, it isfound that such a conventional scheme may have some disadvantages.

For example, in the known lens driving device, the OIS coils formed withthe coil plate are typically different in length and/or are asymmetric.Such difference or asymmetry leads to a yawing effect, which makes thelens assembly and the magnet rotate unintentionally. The rotating of thelens assembly and the magnet will make the displacement sensor fail todetect the displacement correctly, such that the lens driving devicecannot enable the auto-focusing and mage stabilization. Besides, inorder to realize the AF and OIS functions in a greater precision, themagnetic sensitivity of the OIS coil structure needs to be furtherimproved.

SUMMARY OF THE INVENTION

An object of the present invention provides a VCA-based lens drivingdevice with an improved optical image stabilization (OIS) coil structureand improved magnetic sensibility for image stabilization. According tothe present invention, the auto-focusing (AF) function and the OISfunction can be realized by either a common magnet scheme or a separatemagnet scheme. It is also an object of the present invention to providean improved structure for the lens driving device to enhance thefunction of OIS thereof.

Therefore, in one aspect, the present invention provides a lens drivingdevice including a lens assembly having an optical axis, anauto-focusing (AF) coil disposed around an outer surrounding of the lensassembly with respect to the optical axis, a set of optical imagestabilization (OIS) coils disposed on a plane having a normal directionperpendicular to the optical axis, a plurality of magnets arranged abovethe set of OIS coils in such a way that each of the magnets has a firstsurface facing the AF coil and a second surface facing the OIS coils,and a magnetic enhancement device disposed under the set of OIS coils.

Preferably, the magnetic enhancement device includes plural magneticpieces, each of which being disposed under a respective OIS coil of theset of OIS coils. The plural magnetic pieces can be formed with a bottomframe of the lens driving device, or can be embedded in a bottom frameof the lens driving device. Alternatively, the magnetic enhancementdevice is formed by distributing a plurality of magnetic particleswithin a bottom frame of the lens driving device.

Preferably, the lens driving device further including at least onemagnetic induction element for sensing a magnet signal induced by adisplacement of the magnets, and each of the plural magnetic pieces ofthe magnetic enhancement device is disposed under a respective OIS coilof the set of OIS coils or the at least one magnetic induction element.

In another aspect, the present invention provides a lens driving device,including a lens assembly having an optical axis, an auto-focusing (AF)coil disposed around an outer surrounding of the lens assembly withrespect to the optical axis, a set of optical image stabilization (OIS)coils disposed on a plane having a normal direction perpendicular to theoptical axis, a magnet group including a set of first magnets and a setof second magnets, and a magnetic enhancement device disposed under theset of OIS coils. The first magnets are arranged above the set of OIScoils correspondingly in such a way that each thereof has a surfacefacing to the AF coil, while the second magnets are arranged above theset of OIS coils correspondingly in such a way that each of the secondmagnets has a surface facing to the OIS coils.

Preferably, the magnetic enhancement device includes plural magneticpieces, each of which being disposed under a respective OIS coil of theset of OIS coils. The plural magnetic pieces can be formed with a bottomframe of the lens driving device, or can be embedded in a bottom frameof the lens driving device. Alternatively, the magnetic enhancementdevice is formed by distributing a plurality of magnetic particleswithin a bottom frame of the lens driving device.

Preferably, the lens driving device further including at least onemagnetic induction element for sensing a magnet signal induced by adisplacement of the magnets, and each of the plural magnetic pieces ofthe magnetic enhancement device is disposed under a respective OIS coilof the set of OIS coils or the at least one magnetic induction element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a lens driving deviceaccording to a first embodiment of the present invention;

FIG. 2 is a schematic top exploded view of the lens driving device asshown in FIG. 1;

FIG. 3 is a schematic perspective view of a lens driving deviceaccording to a second embodiment of the present invention;

FIG. 4 is a schematic top exploded view of the lens driving device asshown in FIG. 3;

FIG. 5 is a schematic top exploded view for showing the magnetic fielddistribution in the structure as shown in FIG. 3;

FIG. 6 is a schematic perspective view of a lens driving deviceaccording to a third embodiment of the present invention;

FIG. 7 is a schematic top exploded view of the lens driving device asshown in FIG. 6;

FIG. 8 is a schematic perspective view showing an exemplary magneticenhancement device used in the lens driving device of the presentinvention;

FIG. 9 is a schematic perspective view of a lens driving deviceaccording to a fourth embodiment of the present invention;

FIG. 10 is a schematic top exploded view of the lens driving device asshown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the present invention are shown.

The present invention provides a lens driving device that is based on aVoice Coil Actuator (VCA) structure and provides the auto-focusing andoptical image stabilization (OIS) functions. According to the presentinvention, these two functions can be realized by a common magnetscheme, or a separate magnet scheme. Besides, the present invention alsoprovides an improved structure for the lens driving device to enhancethe effect of AF and OIS functions thereof.

Please refer to FIG. 1 and FIG. 2, which are a schematic perspectiveview and a schematic top exploded view showing the lens driving deviceaccording to a first embodiment of the present invention, respectively.It should be noted that some components of the lens driving device arenot shown in these figures, so as to avoid an unnecessary obscuring ofthe present invention. As shown in FIG. 1, the lens driving devicemainly includes a lens assembly 18 having an optical axis, anauto-focusing coil (AF coil) 3, a set of OIS coils 91 x, 91 y, 92 x, 92y, and a plurality of magnets 61 x, 61 y, 62 x, 62 y. In the presentinvention, the optical axis of the lens assembly 18 is defined as theZ-axis for illustration. The AF coil 3 and the magnets 61 x, 61 y, 62 x,62 y are disposed around an outer surrounding of the lens assembly 18with respect to the optical axis. The OIS coils 91 x, 91 y, 92 x, 92 yare disposed on a plane whose normal direction is perpendicular to theoptical axis (e.g. the X-Y plane).

Referring to FIG. 2, each of the magnets 61 x, 61 y, 62 x, 62 y has aninner N pole and an outer S pole. The AF coil 3 and the set of OIS coils91 x, 91 y, 92 x, 92 y share a common magnet set composed of the magnets61 x, 61 y, 62 x, 62 y. In this embodiment, the magnets 61 x, 61 y, 62x, 62 y and the OIS coils 91 x, 91 y, 92 x, 92 y below the magnets aredisposed in such a way that each of the magnets 61 x, 61 y, 62 x, 62 yhas a first surface facing the AF coil 3, and a second surface facing arespective one of the OIS coils 91 x, 91 y, 92 x, 92 y. By suchconfiguration, an electromagnetic driving force will be induced insidethe AF coil 3 by the current passing through the AF coil 3 and themagnetic field generated by the magnet set of magnets 61 x, 61 y, 62 x,62 y, thereby the lens assembly 18 is driven to perform theauto-focusing function. Besides, the current passing through the OIScoils 91 x, 91 y, 92 x, 92 y and the magnetic field generated by themagnet set of magnets 61 x, 61 y, 62 x, 62 y will act to induce afurther electromagnetic driving force inside the set of OIS coils, suchthat the lens assembly 18 may be tuned to perform the OIS function (i.e.the so-called anti-shaking function). Specifically, the electromagneticdriving force induced by the AF coil 3 and the magnets 61 x, 61 y, 62 x,62 y enables the lens assembly 18 to move along the optical axis againstthe change in magnet flux of the magnets 61 x, 61 y, 62 x, 62 y, suchthat the auto-focusing function is realized. The OIS coil 92 x interactswith the magnet 62 x in a direction the same as the direction in whichthe OIS coil 91 x interacts with the magnet 61 x. Also, the OIS coil 92y interacts with the magnet 62 y in a direction the same as thedirection in which the OIS coil 91 y interacts with the magnet 61 y. Insuch a manner, the lens assembly 18, the AF coil 3 and the magnets 61 x,61 y, 62 x, 62 y can move along the directions (i.e. the X-axisdirection and/or the Y-axis direction) perpendicular to the optical axiswith respect to the OIS coils 91 x, 91 y, 92 x, 92 y to realize theoptical image stabilization (i.e. the so-called anti-shaking function).

FIGS. 3 to 5 schematically illustrate a lens driving device according toa second embodiment of the present invention, wherein FIG. 3 is aschematic perspective view of the lens driving device, and FIGS. 4 and 5are schematic top exploded views showing the components and thedistribution of magnet field of the lens driving device respectively. Inthis embodiment, the AF function and the OIS function of the lensdriving lens are realized by a separate magnet scheme.

Referring to FIG. 3, the lens driving device according to thisembodiment mainly includes a lens assembly 18 having an optical axis, anauto-focusing coil (AF coil) 3, a set of OIS coils 91 x, 91 y, 92 x, 92y, and a magnet group. The magnet group includes a plurality of AFmagnets 63 x, 63 y, 64 x, 64 y and a plurality of OIS magnets 65 x, 65y, 66 x, 66 y. As shown in FIG. 3, the AF coil 3, the AF magnets 63 x,63 y, 64 x, 64 y and the OIS magnets 65 x, 65 y, 66 x, 66 y are disposedaround an outer surrounding of the lens assembly 18 with respect to theoptical axis (i.e. the Z-axis). The OIS magnets 65 x, 65 y, 66 x, 66 yare positioned below the AF magnets 63 x, 63 y, 64 x, 64 y,respectively, and the OIS coils 91 x, 91 y, 92 x, 92 y, which aredisposed on a plane having a normal direction perpendicular to theoptical axis (e.g. the X-Y plane), are positioned under the respectiveOIS magnets 65 x, 65 y, 66 x, 66 y. The OIS coils 91 x, 91 y, 92 x, 92 yare arranged to sequentially face the respective OIS magnets 65 x, 65 y,66 x, 66 y.

Referring to FIGS. 4 and 5, each of the AF magnets 63 x, 63 y, 64 x, 64y has an inner N pole and an outer S pole. An electromagnetic drivingforce is induced in the AF coil 3 by the current passing through the AFcoil 3 (the AF current) and the magnetic field generated by the AFmagnets 63 x, 63 y, 64 x, 64 y, to perform the AF function. Besides, inthe set of OIS coils, an electromagnetic driving force is induced by thecurrent passing through the OIS coils 91 x, 91 y, 92 x, 92 y (the OIScurrent) and the magnetic field generated by the OIS magnets 65 x, 65 y,66 x, 66 y to perform the OIS function (i.e. anti-shaking function).Specifically, by interaction of the AF coil 3 with each of the AFmagnets 63 x, 63 y, 64 x, 64 y, the AF coil 3 and the lens assembly 18can be moved along the optical axis with respect to the AF magnets 63 x,63 y, 64 x, 64 y, such that the auto-focusing operation is carried out.The OIS coil 92 x interacts with the magnet 66 x in a direction the sameas the direction in which the OIS coil 91 x interacts with the magnet 65x. Also, the OIS coil 92 y interacts with the magnet 66 y in a directionthe same as the direction in which the OIS coil 91 y interacts with themagnet 65 y. In such a manner, the lens assembly 18, the AF coil 3, theAF magnets 63 x, 63 y, 64 x, 64 y and the OIS magnets 65 x, 65 y, 66 x,66 y can move along the directions (i.e. X-axis direction and/or Y-axisdirection) perpendicular to the optical axis with respect to the OIScoils 91 x, 91 y, 92 x, 92 y to perform the OIS function (i.e.anti-shaking function).

Due to the fact that the current induced in a coil, such as an OIS coil,depends on the changing in the strength of magnetic field and thus thedensity of magnetic flux, it is advantageous to improve the magneticsensitivity of the lens driving device by increasing the density ofmagnetic flux, so as to offset the shaking effect in a greaterprecision, and to further stabilize the optical image. The powerconsumption required for anti-shaking function can be reduced as well.For this purpose, the present invention also provides an improvedstructure for the lens driving device, in which the distribution of themagnet field as generated can be more concentrated, and the magnetsensitivity for the anti-shaking function will be improved accordingly.

Please refer to FIG. 6 and FIG. 7, which are the schematic perspectiveview and the schematic top exploded view of a lens driving deviceaccording to a third embodiment of the present invention, respectively.In this embodiment, the lens driving device is also a VCA-based lensdriving device and has a similar configuration as shown in FIGS. 1 and2. Please note that the AF coil 3 (as shown in FIGS. 1 and 2) is omittedfrom FIGS. 6 and 7 for clarity. The present lens driving device mainlyincludes a lens assembly 18 having an optical axis, an auto-focusingcoil (AF coil) (not shown), a set of OIS coils 91 x, 91 y, 92 x, 92 y, aplurality of magnets 61 x, 61 y, 62 x, 62 y, and a magnetic enhancementdevice 12. The lens driving device may optionally include at least onemagnetic induction elements such as Hall sensors 100 x and 100 y tosense a magnet signal induced by a displacement of the magnets 61 x, 61y, 62 x, 62 y. The optical axis of the lens assembly 18 is defined asthe Z-axis for illustration. The magnets 61 x, 61 y, 62 x, 62 y aredisposed around an outer surrounding of the lens assembly 18 withrespect to the optical axis. The OIS coils 91 x, 91 y, 92 x, 92 y aredisposed on a plane whose normal direction is perpendicular to theoptical axis (e.g. the X-Y plane). In this embodiment of the presentinvention, the magnetic enhancement device 12 is disposed below andcovering the set of OIS coils 91 x, 91 y, 92 x, 92 y and Hall sensors100 x, 100 y, so as to enhance the magnetic sensitivity of the lensdriving device. In more specific, the magnetic driving force of the OIScoils 91 x, 91 y, 92 x, 92 y and magnetic induction of the Hall sensors100 x, 100 y can be enhanced because the lines of magnetic force of therespective magnet atop the OIS coil and the magnetic enhancement devicebelow the OIS coil is more concentrated at the OIS coil, such that themagnetic sensitivity of the OIS coils may be improved.

In the present invention, the magnetic enhancement device may be madefrom magnetic materials including, but not limited to, magnetic metals,alloys and/or ferromagnetic or ferrimagnetic materials. Please notethat, by dispersing the magnetic particles in a bottom frame of the lensdriving device, or by coating the bottom frame of the lens drivingdevice with a magnetic layer, the bottom frame that is intrinsicallynon-magnetic can function as a magnetic enhancement device of thepresent invention. Alternatively, the plate-like magnetic enhancementdevice 12 as shown in FIG. 6 is provided as a bottom frame of the lensdriving device of the present invention.

Please refer to FIG. 8, which is a schematic perspective view showing analternative exemplary magnetic enhancement device used in the lensdriving device of the present invention. The magnetic enhancement device120 as shown is a plate-like unitary piece, on which some portions maybe removed (for example, by cutting) to form spaces 120 x, 120 y foraccommodating the Hall sensors 100 x, 100 y. It should be noted that,the magnetic enhancement device according to the present invention isshown, in the exemplary embodiments, as being used in the lens drivingdevices with winding OIS coils; however, the purposed magneticenhancement device is also applicable for the FP-coil structure. Thatis, instead of the OIS coils as shown in the exemplary embodiments, atypical flexible printed circuit board, having FP-coils formed thereonand controlled by the flexible printed circuit, can be used in the lensdriving device of the present invention, and in such a case, it may beadvantageous to have the magnetic enhancement device 120 correspond tothe flexible printed circuit board in shape. Alternatively, the magneticenhancement device of the present invention can be formed as includingplural magnetic pieces, and each of which is disposed as correspondingto the respective FP-coil on the flexible printed circuit board, or isdisposed under a respective OIS coil, which will be further illustratedbelow.

Please refer to FIG. 9 and FIG. 10, which are the schematic perspectiveview and the schematic top exploded view of a lens driving deviceaccording to a fourth embodiment of the present invention, respectively.In this embodiment, the VCA-based lens driving device has a similarconfiguration as shown in FIGS. 6 and 7, except the magnetic enhancementdevice. As shown in FIG. 9, the magnetic enhancement device includesplural magnetic pieces 12 x, 12 y, 13 x, 13 y, 14 x, 14 y, which arepositioned below the OIS coils 91 x, 91 y, 92 x, 92 y and the Hallsensors 100 x, 100 y, respectively. The current passing through therespective OIS coils 91 x, 91 y, 92 x, 92 y is indicated by the arrow asshown. Also, the magnetic driving force of the OIS coils 91 x, 91 y, 92x, 92 y and magnetic induction of the Hall sensors 100 x, 100 y can beenhanced because the lines of magnetic force of the respective magnetatop the OIS coil and the respective magnetic piece below the OIS coilare more concentrated at the OIS coil, such that the magneticsensitivity thereof may be improved.

It should be noted that, the configuration of magnetic enhancementdevice as shown in FIG. 6 through FIG. 10 is only provided forillustration with respect to the lens driving device whose AF and OISfunctions are realized by a common magnet scheme. Nevertheless,according to the present invention, the magnetic enhancement device isalso applicable in the lens driving device whose AF and OIS functionsare realized by a separate magnet scheme, such as the lens drivingdevice as shown in FIGS. 3 to 5.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and thatstructures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A lens driving device, comprising: a lensassembly having an optical axis; an auto-focusing (AF) coil disposedaround an outer surrounding of said lens assembly with respect to saidoptical axis; a set of optical image stabilization (OIS) coils disposedon a plane having a normal direction perpendicular to said optical axis;a plurality of magnets arranged above said set of OIS coils in such away that each of said magnets has a first surface facing said AF coiland a second surface facing said OIS coils; and a magnetic enhancementdevice disposed under said set of OIS coils.
 2. The lens driving deviceaccording to claim 1, wherein said magnetic enhancement device includesplural magnetic pieces, each of which being disposed under a respectiveOIS coil of said set of OIS coils.
 3. The lens driving device accordingto claim 2, wherein said plural magnetic pieces are formed with a bottomframe of said lens driving device.
 4. The lens driving device accordingto claim 2, wherein said plural magnetic pieces are embedded in a bottomframe of said lens driving device.
 5. The lens driving device accordingto claim 1, wherein said magnetic enhancement device is formed bydistributing a plurality of magnetic particles within a bottom frame ofsaid lens driving device.
 6. The lens driving device according to claim1, further comprising at least one magnetic induction element sensing amagnet signal induced by a displacement of said magnets.
 7. The lensdriving device according to claim 6, wherein said magnetic enhancementdevice includes plural magnetic pieces, each of which being disposedunder a respective OIS coil of said set of OIS coils or said at leastone magnetic induction element.
 8. The lens driving device according toclaim 1, wherein said OIS coils are winding coils or coils that areformed on a flexible printed circuit board.